Magnetrons



March 1959 M. ESTERSON ETAL MAGNETRONS Filed March 14, 1958" F/GJ uINVENTQRJ 77 MW g- 4%7m @zmw 36% W ATTORNEYS United States PatentMAGNETRONS Maurice Esterson and Alec Peter Orme 'Collis, Essex, England,assignors to English Electric Valve Company Linuted, London, England, acompany of Great Britain Application March 14, 1958, Serial No. 721,374Claims priority, application Great Britain April 26, 1957 2 Claims. (Cl.SIS-39.61)

This invention relates to magnetrons and more specifically to multipleresonant cavity tunable magnetrons of the kind in which tuning isaccomplished by means of conductive pins carried upon an adjustableconductive carrier member and which project into the resonant cavitiesto an extent which can be altered by altering the position of thecarrier member carrying the pins.

The invention is illustrated in and explained in connection with theaccompanying drawings in which Figure 1 is a highly simplifieddiagrammatic representation of a known magnetron of the kind to whichthe invention relates and Figures 2 and 3 are mutually perpendicularviews of a tuning assembly comprising a set of tuning pins with theircarrier member as used in one embodiment of this invention.

Referring to Figure 1 this represents a multiple cavity magnetron ofgenerally known form with a cylindrical cathode structure 1 coaxiallywithin the usual anode system which is provided with resonant cavities 2in a ring round the cathode.

The anode block is drilled parallel to the axis to take tuner pins 3 oneof which extends into each resonant cavity (except the cavity providedwith an energy takeoif loop in magnetrons in which there is such acavity) to an extent which can be adjustable for purposes of tuningvariation. The magnetron represented in Figure 1 is of the strappedtyped, straps being indicated at 4. The tuner pins are carried on acarrier disc 5 which can be adjusted in the axial direction by means ofa lead screw member or nut 6. The screw is external to the evacuatedspace of the magnetron, vacuum being preserved by means of a flexiblediaphragm 7 which completes the evacuated space and permits the requiredaxial movement for tuning.

This known magnetron is reasonably satisfactory but it has the defectthat spurious resonances are apt to occur at different frequencies inthe tuning range. These spurious resonances reduce the output power andincrease the liability to internal flashing at tuning positions in whichthe spurious resonance tuning curves cross the curve of anode tuning.

Although most spurious resonances can be kept out side the workingfrequency range by suitable choice of end space and other dimensions, ithas been found by experiment that most persistant resonances areassociated with the tuner pins themselves and are critically dependentupon the clearances between the pins and the resonant cavity wallsthrough which those pins pass. It is extremely difiicult in practicalmanufacture to keep these clearances at the same required values frommagnetron to magnetron with the required precision. Because of this itis in practice common for diiferent magnetrons of the same design andwhich should give the same performance in fact to give considerablydifferent performances. This is a serious defect which it is the objectof the present invention to eliminate or reduce.

Experiment has shown that objectionable spurious resonances occur due tovoltages which are induced in the tuner pins causing currents to flowaxially along the pins and around the carrier disc by which they aresupported. These resonances are very dependent on small displacements ofthe entire pin and carrier assembly, for example on small rotationsabout the axis.

According to this invention the tuning pin carrier member of a multipleresonant cavity tunable magnetron of the kind referred to is slottedbetween successive pairs of tuning pins (counting round the carrier) sothat successive pairs of pins are divided off from one another by aslot.

Preferably the carrier is a disc with radial slots therein.

Figures 2 and 3 show one form of construction of tuner assembly for usein a magnetron in accordance with this invention.

Referring to these figures the tuning assembly therein shown comprises aring of metal tuner pins 3 mounted on and at right angles to a metalcarrier disc 5 provided with a lead screw member or nut 6. The assemblyas so far described is as well known and is mounted in the magnetron inthe manner shown in Figure 1 or in some similar known manner so thateach pin projects into one of the cavities of the anode system to anextent which can be adjusted by adjusting the whole assembly axially ofthe magnetron.

In accordance with this invention slots 7, 7a extending radially of thecarrier member 5 are provided with each slot being between successivepairs of tuning pins counting round the carrier, so that each pair ofpins is between two slots. In the particular construction shown inFigures 2 and 3 one of the radial slots-that designated 7a and shown atthree oclock in Figure 3-is made much wider than the others, 7, and isalso tapered. This is for a reason which has nothing to do with thepresent invention as such but is merely because, in the particularmagnetron for which the tuning assembly of Figures 2 and 3 is designed,the wide slot 7a is necessary in order to clear a part of the magnetronstructure used for supporting the cathode. The widening of thisparticular slot 7a is thus, as it were, fortuitous, and if it were notnecessary to provide a clearance this particular slot would be like theothers. Also in the construction shown in Figures 2 and 3 the pins donot occur at regular intervals all round the carrier member 5, therebeing a considerably larger space between the two pins shown at the topof Figure 3 than between any other two pins. As will be seen thisconsiderably larger space corresponds to the omission of a pin which, ifthe required spacing was equal throughout, would be provided at 12oclock in Figure 3. This omission has again nothing to do with thisinvention as such, but is due to the fact that, in the particularmagnetron for which the tuning assembly of Figures 2 and 3 is designed,one of the resonant cavities (that corresponding in position to theomitted pin) contains an energy take-oil loop and, of course, no tuningpin is provided to enter that cavity. The pins 3 shown in Figures 2 and3 are hollow but, of course, they could be solid.

We claim:

1. A multiple resonant cavity tunable magnetron having a tuning pincarrier disc and a plurality of tuning pins carried thereon, said dischaving a plurality of radial slots respectively extending between anddividing successive pairs of tuning pins from one another.

2. A multiple cavity magnetron comprising a cathode and an anode systemco-axial with said cathode and having a plurality of resonant cavitiesin a ring round the axis, each cavity extending parallel to said axisand opening into an interaction space co-axially within the anodesystem, said anode system including a conductive disc carrier member atright angles to said axis, a plurality of parallel conductive tuner pinscarried by said carrier member and extending parallel to said axis andentered respectively into said cavities, said carrier member having aplurality of slots lying along radii of said carrier member and betweensuccessive pairs of said tuning pins, and means for adjusting saidcarrier member longitudinally of said axis to adjust the positions ofsaid tuning pins longitudinally of said cavities.

References Cited in the file of this patent UNITED STATES PATENTS

